ol. 56.] MR. F. W. 



HARMER ON THE CRAG OF ESSEX. 713 



Trochus noduliferens. 





Lucina borealis. 



subexcavatus. 





Cardita corbis. 



Adansoni. 





scalaris. 



Montacuti. 





senilis. 



Fissurella grceca. 





Cardium edule. 



Emarginula fissura. 





Parkinsoni. 



Calyptrcsa chinensis. 





Gyprina islandica. 



Capulus ungaricus. 





Astarte obliquata. 



Teetura virginea. 





Galeottii. 



ActcBon Nocb. 





Burtinii. 



Conovulus pyramid alts. 





Woodia digitaria. 



Anomia ephippium. 





Artemis lentiformis. 



Ostrea cochlear. 





Mactra arcuaia. 



Pecten opercularis. 





Solen ensis. 



■ pusio. 





siliqua. 



Mytilus edulis. 





gladiolus. 



Pectunculus glycimeris, 



especially 



Corbula gibba. 



var. subobliquus. 





Corbulomya complanata. 



Nucula IcBvigata. 





Pholas crispata. 



Montacuta bidentata. 





cylindracea. 



Scintilla ambigua. 







The majority of the foregoing species are either extinct or southern forms. 



A number of northern or recent species, which became more or 

 less common in the later beds of the Red Crag, are moreover absent 

 or rare at Walton ; of these I may mention : — 



Buccinum groenlandicum. 

 Trophon (Neptunea) antiqrms 



(dextral). 



despeclus. 



scalariformis. 



alius. 



Purpura lapillus (the existing 



form). 

 Cancellaria viridula. 

 Turritella terebra. 

 Scalaria groenlandica. 

 Littorina littorea. 

 Natica clausa. 



catena. 



grmilandica. 



Trochus formosus. 



tumidus. 



Modlola modiolus. 

 Nucula Cobboldice. 



tenuis. 



Leda oblongoides. 



lanceolata. 



Cardium angustatum. 



groenlandicum. 



Astarte compressa. 



sulcata. 



Tellina obliqua. 



prcstenuis. 



Mactra ovalis. 

 constrict a. 



None of the foregoing species are known from the Crag of Normandy, or 

 from any Older Pliocene beds south of Great Britain. 



A very few specimens only of some of them have been fonnd at 

 Walton ; but they are the rare exceptions, not the rule, and were 

 the vanguard, so to speak, of the molluscan army which at a 

 subsequent period invaded the Crag basin from the north. 



Adopting, as I have always done, Wood's opinion as to the com- 

 paratively early age of the Walton Crag, and its marked distinction 

 from that of Suffolk, it seemed to me important, as a crucial test 

 of the hypothesis that the upper Crag deposits were the littoral 

 accumulations of a sea gradually retreating northward, to re-examine 

 the district between Walton and the estuary of the Stour, in order 

 to see whether any beds of intermediate character could there be 

 found, which might serve to bridge over the gap separating the 

 Walton Crag from that of Suffolk. 



